This invention relates to a method of emission spectrochemical analysis which can determine the quantitative analysis of other elements in a metal.
In metallurgy, such a measurement is usually taken to determined a specified element which has been added into a metal for the purpose of improving some property the metal, degassing, purifying, or arranging the particle size of crystals of the metal, etc. In the case of steel, for example, aluminum is added to steel for the purpose of turning the steel into a non-aging steel through removing the oxygen in the steel or stabilizing the nitrogen in the steel. It results in that the steel includes a hemogeneous type of Al mixed with steel uniformly into an alloy and a heterogenous type of Al as scattering in the texture of steel in the form of aluminum oxide (Al.sub.2 O.sub.3).
As for the latter, the aluminum oxide scattering in the form of heterogeneity is generally not a favorable constituent of steel and specifically larger particle sizes of aluminum oxide or scattered groups thereof deteriorate the mechanical properties of the steel.
The properties of steel vary depending on the ratio of the homogeneity to the heterogeneity even if the total quantity of Al in the steel is the same. It is necessary, therefore, to control the ratio of homogenious to heterogenous Al as well as the total quantity of Al in steel, and thus, this kind of quantitative analysis is required.
The quantitative measurement by the emission spectrochemical analysis can be made more speedily performed than by means of chemical analysis and it is possible to allow favorable treatment in the quality control or process control of steel by controlling the required quantity of Al to be added to steel. Thus, the method of analysis mentioned above has been adopted to determine the total quantity of mixed elements and their existing state.
Emission spectrochemical analysis can determine the quantitative analysis of mixed elements in a specified metal as well as their existing state on the basis of the principle that a sample produces an emission with spark discharging. The specified elements are detected through the spectrochemical analaysis wherein although the intensity of emission varies in each emission, strong intensity of emission is seen many times in the first stage of the repetition of spark discharging and then as time passes the accompanying strong intensity of emission is decreased and the variation of the intensity of emission becomes less. The difference between the mean of each intensity of emission seen in the first stage and that of those seen in the stabilized or later stage relates to the ratio of the homogeneity to heterogeneity.
The phenomenon mentioned above exhibits a large intensity of emission when a spark discharging arises between the electrode and the element mixed in a sample in a heterogeneous condition and thereafter the heterogeneous matter will not emit so strongly even when subjected to a spark discharging on account of vaporization, dispersion with fine differentiation, etc,. However, it is hard to make an accurate analysis in this case as even homogeneous elements exhibit the tendency of the dropping of intensity of emission as the spark discharging is repeated.
A method of quantatitive analysis is shown in U.S. Pat. No. 3,876,306 wherein the light volume of the specified element including its homogeneous state and its heterogeneous state is obtained through the spark discharging between a sample and an electrode. The light volume is converted into a current of light, the total photoelectric current of the element is integrated, the value of the photoelectric current of the homogeneous state is integrated on the basis of the mean of the photoelectric current of the homogeneous state among those products of the specified element mentioned above, the difference between the former integrated value and the latter integrated value is calculated, and thus the content of said specified element in the sample in its homogeneous state and its heterogeneous state are separately determined. This method is not, however, satisfactory from the viewpoint of its evaluation in accuracy, etc.
Although the analyzing method mentioned above can be carryied out in less time in comparison to chemical analysis, it still takes several tens of seconds of time and the reproductivity of its measured result and the accuracy of analysis are not good. This is due to the fact that the variation of the intensity of emission through the spark discharging is not stable and the same result is hard to obtain even with the same sample.